Right-left indicating direction finder system



Sept. 14, 1943. E. J. HEFELE 2,329,199

RIGHT-LEFT INDICATING DIRECTION FINDER SYSTEM Filed 001;- 2. 1935 4Sheets-Sheet 2 ATTORNEY.

Sept. 14, 1943. E. J. HEFELE 2,329,199

RIGHT-LEFT INDICATING DIRECTION FINDER SYSTEM Filed Oct. 2, 1935 4Sheets-Sheet 3 a W. w as; W I

INVENTOR. Gdwardj Jtef'ele BY a E E I ATTORNEY Ill IllW////W//////////4v Sept. 14, 1943.

E. J. HEFELE 2,329,199 RIGHT-LEFT INDICATING DIRECTION FINDER SYSTEMFiled Oct. 2, 1935 4 Sheets-Sheet 4 INVENTOR. 'dwara'j. J('fle BYATTORNEY.

of theloop and. is unaffected by Patented Sept. 14,1943

" 1 UNITED STATES? RIGHT-LEFT mmoA mG miiEoirm L I V'FVINDEBISYSTEM kEdward-J. nefelanmityviue,NQY; I a

My invention relates to radio: direction finders, and more particularly,to that type of direction finder that automatically indicates thedeviation .in bearing to the right or left of thedeslred direction. I iThe determining factor in the directional function of the usualdirection finder with aloop; antenna is the orientation or angularposition of the ".loop with respect to the direction of *the receivedsignal. 'The null point is detected by -a sharp demarcation between adecreasing and increasingsignal reception according to. the angularposition of the-loop. Accurately controlled frequency, amplification orother electrical :con-

ditions in the associated apparatus, are unneces the indicateddirection. Thus the directionalacproducinga resulting indicationwhich'was either y -to the rightor tostheleft of the zero center.

There areseveral disadvantages inherent in: thissystem;.: :There' are;four directional indicaf tions Obtainable-fQreach resultant signalstrength throughout the -range.of:'360-- azimuth with re'-specttdthegtransinitting source, resulting'ina 90 15.- .sarysince theydo not-{affect the accuracy of curacy of loop reception depends solelyupon-the f geometry of the loop, 1. e., the angularfpo'sition variationsof the electrical constants. Y 1 =2:

In numerous situations. such as in aeroplanes,

however, direction finders are insufficientzduei to the experimentalwork necessary in rotatingjthe loop back and forth to :find the-null'or"-maxi-- mum. For-these' cases, ithas been proposedto use a right leftindicator, a system infwhich bearings are obtained automatically.' g

In right left indicators proposed heretofore, however, the readingsdepended upon constancy Thus the over-.all amplification or gain of ,the

such" a direction .in'strumentn and commercially impractical. A

jrslight in'isadjustment in either 100p circuit'results in :err'ors' of"as much astsix r seven degrees. fI'ests have shown that suchequipmentis entirely I unreliable under normal operating conditionssorithe ground; on shipboard or in an aircraft? Mme electrical conditions ofthe. circuit, a factor which is in'ipossible to obtain, and accordinglyno commercially practical right left indicator system has heretoforebeen developed.

-;An early attempt at imparting a right andvlef-t sense totherdirectionfinder was toutilize two loop antennae placed at an angle to each; other'(usually' 90), two radio receivers, and. a'difierentially connectedindicating meter. The normal jfigure-of-eight polar pattern defined therecep- I tion of [each loop and associated amplifier independently. Whenthe loops were in on-course position, equal signals are received by themand therefore equal outputs'lwould be fed tolthe differ'entiallyconnected output meter. Thi meter was-connected so that the equaloutputs produced equal andv opposite" deflecting torques upon the The,nextdevelopment in the art was to remove a major disadvantage byutilizing. only one radio r receiven-gjl' hec-ompcnent of' this systemalso V H consisted of two, loop antennae placed at :an

angle with respectto each. other, a single radio Zreceiver,di-fierentially; connected indicating a -meter, and'a switching devic'ewhich alterr a'telw I connectedeitherloop to the radio receiver and atthe same time switched theecorresponding ternimals of theindicatingmeter to the outputgof indicating needles, which resultedin aZero cen- I .ter or fon-coursefreading. "If ith-B line ofbearing was toeither therightlor-leftxof thetrue radio bearing one of the loop signalspredomi-- .nated and the receivers thus had unequal inputs appliedtothem fromthe loopantennae: There resulted-unequal outputs to theindicating meter,

."twodoop' principle and utili ze but a sin led c They consist essenti ugora iocpiantennag a; ,-sma11;,veru a1 antenna; an electronic switching"mechanism/a radio receiver and a-difierentially I indicating meterl' 'Ihelo'op antennaandithev'eri 7 thus entirely 40; i V I i chanicalswitching introduced transient, voltages theraclio receiver. Thenecessity. of maintaining the sensitivity-of; two radio receive rs equaLwas removed. Various switching schemes.- were tried but-fit was foundthatxmee tolthe radioreceiver which resulted in. erratic; I I operation.2 .ElfiCtibnic. switching was thendeveloped to avoid theobjectionabletransielit i. f However, bearing inaccuracies jresulting from slightmi'sa'djustments in' either loop: circuit together warn the so ,beaiingambiguity. make such right "left indicator systems impractical,especially for an ler-times 50"" The T more "recent developments" departfro ing reasons.

tical antenna are alternately connected to produce a cardicid polarpattern of reception first 7 having the null direction towards the rightand then towards the left of the direction of motion. The switchingmechanismis arranged to alternately apply such right and left handcardioid reception patterns to the radio receiver. An oncourse bearingproduces equal signal inputs to the receiver, so thatuthere is :aresultant zero torque on the needle of the difi'erentiallyconnectedindicating meter. This schemeis a great improvement over previous typesof right and left,

mu e er percentage of the effective height-of the 1 loop j; antenna isutilized, resulting in a higher signal to static noise ratio whichpermitsbearin to indicating direction finders.

be taken when the null type direction finder would not be usable. 180bearingambiguity is' eliminated since when the aircraft is'recedingvfrom instead of approaching the radio transmit ter, the right-left senseindication .beco'mes reversed. Only one. loop antenna is employed,"reducing the loop' system aerodynamic resistance by approximately'fiftyper cent; .Several serious disadvantages nevertheless Mmeke :thi'sdirection .;changes in. the electrical constants have occurred; sothatlie' may make adjustments. 1; 3:1;

EInth'e Kruesi systemgfor examplegPatentNo. 1,868,945, if Ithe loop ismistunejd "by as; little as finder extremely unreliable. Where it isthe'sole navigational instrument, as is oftenfithecase electricalparameters. 7 -=va riabl-es may be adjusted accurately at a singlefrequency and for a. given set of temperature humidity and electricalconditions, but when these critical adjustments change because ofvariations'of the original conditions, large errors indirectionalaccuracy result. What is more serious, the-operator is not apprised thatthese one per cent, a three or four degree material -erro'rr' resultssince the indication obtained depends upon a" comparison of the signalpick-up when an aircr'aftis flying throughfog; this .un- 1 reliability 1is dangerous because-ofizthei fact? that the indicating meter willcontinue :to indicateright and left even though the bearing maybe inserious error; with no wayttonthe' operator to test for or realize'theerror.

. In the practical application of apparatus; adjustments must be madevery ofteneven with.-

:of the loop withthe signalpick-up of the vertical :ant'enna. Atwoperrcent mistun'ing erronawhich a very likely practical tuningvariation; .will lproduce an indicated deviation :fromnormal to such anextent that although the [ship :may be onxits proper course, there? willbe indicated a the most carefully.designedlequipment. Altuned to producethe. required cardioidpolar reception patterns since this "combinationis most satisfactory from the standpoint ofv sensitivity with the use ofthe present radio receivers. This-most loop circuit and an aperiodicVertical antenna circuit with resistance phasing is generally usedadvantageous antenna combination is the sourc of these serious errorsmentioned for the follow- In order to produce the" required cardioids,it is necessary to have properly phased loop and vertical antennacircuits. Inoperation, the loop must be exactly in resonance with-thesignal frequency and be exactly in tune with an extremelyselectivereceiver. An extreme degree of frequency stability is thusrequired in the receiver, and it must therefore notbeaifcted by'temperature changes, supply voltage changes,

and other conditions that alter the receiver calibration. Temperaturecontrol of the radio receiver-has been tried. However, it should'benoted that the lcop'is mounted in the; open air,

' which in itself 'removes any advantages' dueto. receiver temperaturecontrols Thisis particularly true in aircraft'where changes as] great as2 F. per minute mayoccur; whichact to change the electrical tuningcharacteristics of the loop.

Fromthe above it'jwill be noted thatin'lall'the prior right and leftindicators, whether. two loops,

a loopand a vertical antenna, or' asingl e'loopis used} theoperationidepends upon a -comparison of the relative signal pick-upofoneloop; and. the pick-up of either another loop or-ve-rtical; an-

tenna.- A comparison ofsignal strengths either arithmetically or-bybratio; depends upon 1 the absolute values of the resultant signalintensities. These intensities in turn are dependent upon electricalcircuit conditions such as signal-pickup of the loop, thetuningof'therloop circuitjthe gbeen' .utilizedpas indicators inseveralbjtypestof .direction'-finders. For example; two perpendicularloop antennae receive signals which are amplified by two correspondingamplifiers and -are;applied,to the twocorrespondingly perpen wideoff-coursetdirection. In this, asin" the other -cardioid systemsemploying a loop, 'mi'sphasing or' 'mistuning of the loop produceslanimperfect -car'dioid leading to.v erroneous "indications; and

there'is n'o'wayis for the operator to detect this i In general, myinvention M left directional system in iwhich signalsifrom anon-directional antenna and loop antenna are eimpr'es'sed across thevertical and horizontal deflctin'gni'plates respectively of a cathode:ray tube. Lam aware that cathode-ray oscillographs have dicular pairs:of deflecting plates of a flcathoderay-tube. The angular positionofvtheflresultant straight line image on the'fl uorescent screencorresponds to the. angular position of; the loop antennaevi rithrespectto the direction oflthe receive'd signal. l. However,heretheindicationwde; pends-solely uponthe reception and maintenance ofa proper. ratio of signal voltages as intercepted. bytwo antennaeancl'the practical inaccuracies of unbalanced loops, mistuning, unequalampli fication, etc result in false bearings. Another application isthat of Bailey ,PatentNo. "1,833,290 ,where two perpendicular loops] anda co-axial yertical' antenna present three findepend'entek- "rials to":three interdependent amplification and rectificationsystem's, toactuate the two pairs of deflecting plates of' the cathode ray tube.,I-lere to'o, vagaries of tuning and unbalancedlampline .cation resultin ifalseindications. T0"

Since theappliedsignals are of the same as} quenc'y, a'stationaryg'eometric image will result upon the fluorescent screen of;the oscillograph, "-ashereinafter described in detail; When; the.signals are in phase or in opposite phase relation, a straight lineimage results. In casemisph'asi'ng contemplates a 'rig ht a 'we 1Figures. is a sectional view-of streamlined "Qf'thef signal components sems, this is imm A I t loop antenna .o 7-.

tion is revealed by a vertical line imageffiAhorig re" 9{ illustratezontal component of a magnitude dependent upon I the angular position ofthe loop with respect to" the direction of the signaltransmitter,combines v with the non-directional or relatively fixed ver- 'ticalcomponent to produce a straight linezirnage' a at an angle to thevertical. The 'inclination of the image to verticalis to the right .orleft accord-" I be'nt around to reduce its overall length; H

*Incarrying out myinventioml employa s m"- ingto the deviation of theship bearingfrom the t -on-course direction. Automatic grightand "leftdirectional indication is'thus provided with im-- 'mediate, detectionand correction of misphasing and independent of any maintenance'of theratio "of the signal voltages impressed Jon the two antennae; The fulleffective height of the antenna system is used. No; bearing ambiguityexists sincea reversed right and left sensefoc'curs forareciprocalbearing as hereinafter explained. To reduce the aero-dynamicresistance of vthe loop antenna, my invention provides a stream" linedloop antenna system for particular application to aircraft.

fprovidea novel right and left indicating radio direction finder; r t

Anotherobject of my invention is'to provide ajnovel right and leftindicating radio direction finder that has no bearing ambiguity.

1 A further object of my inve'ntionis to provide fanovel right and leftindicating fradio'direjc- *tion finder that is independent ofmisph'a'sing.-of 1 for detectthe loop signal and a novel'method ing andcorrectingthis conditionil' 'A;still further object of my invention isto rq- V vide a novel right and left indicating radio dij- Accordingly,an object of my invention is to rection finder. that functionsindependently of the maintenance of any ratioofvoltages of the-rec'eivedsignal in the apparatus. 1

Another object of my invention is to' provide 'a novel right and leftindicating radio direction 7 finderthat is independent of anyvariationsin the electrical circuit characteristicsfof the s ysterm. I l

Still another object of my:-

,ft' ie i i ee it e- 2a shows ch Eve 1:-

inventionis to rovide a novel right and left-indicating radiofclirection finder that is simple to operate,.reliab le and foolproof. VL 7 Still a further object of my invention, is to provide a novelloopantennasy'stem. 1 ,A further object of my invention is vide a novelloop antenna system ,with'a streamlined body to present a minimumaerodynamic resistance. I

' loopantenna jlfl, it will beainplified and produce I and'form thestraight line horizontal image 25 There are other objects of myinvention, which together with the f0regoing, will appear in thedetailed description which is to follow 'gs-in con-' nection'with thedrawing, in which: Figure 1 is a schematic circuit diagram trating onemodification of my invention.

Figures 2a and'Zb are certain indicator images a that occur in theoperation of my invention.

Figures 3a, 3b and 3c'arenormal' views of the indicator. 7 L i Figure 4-shows a preferred embodiment of lthe indicator screen.-

Figure 5 is a schematic'circuit diagram illus tratinganothermodification of my invention.

l ingthe "right and left indications; A; separa e complete rightandleft-indicating direction 'fin Figure-.7 is a "preferredcircuitdiagrfam for a -i 1 ing systemaccording' to my invention; I

I fmo'dified connection 'agram ror the!cathode hay tuhei s a novicathode ra tub: """the .d'e'fiecting, Q 1

using shield screen's betwee .p at s- :1 Figure 10 shows another novelcathode ray tube:

mar en-1y balanced -1oop antenna I i]: 11713 which isltuned' ,to "thesignal ifre'quency by means l of the shunt variable'mondenser. l4, andyis'jconf- 'nectedtq theinput I 2 I of atuned radio frequency amplifiertrain l 3; The; output 12s [of the loop amplifier}! 3 isconnected tothe''horizontal deir fiecting plates lfifandliifof acathode-r'ay'osj f tlogra'phtube I9. A$I 0Iid1antenna I l,-whichhas I n'on-directlionalreception characteristics, such ajs a vertical'niash' is connected totheinputfzl o f'g is satisifactor invent on l l. qfieq fq i i liw ll indu ea' aee in'th non-directional antennafll whic voltfamplified bytheamplifier p topr y deja I l a. i t utput'zz s es n q d icf mhralub asto produceja verticalj line image onthe fiuoresk c nt 59 1 r iihel a hedr it iu l9;

"cal image" at line24 as it appears'On the scr e'n 230f the cathoderayoscillograph w tent Qfijthi sl image line ".zfdepend upon t streag'th offthe r'eceivedfsignal' in the antennathefeffectivexamplification"ofits amplifier a the deflection sensitivityof the cathode ray tube f l9, Similarly; when a signal is received bythe f a "horizontal; deflection of the cathode ray. beam renderedtemporarilyinoperative. i v

In' the following mathematical analysis of my sinvention, I shallzn'glctthe n'lodu'lation of- -the iradio frequency, carrier. vof the signals.A'si Will beevident, the modulation of the carrierdoes not 7 in "any Wayaffect; the operation of the indi'cations because *both fthe'horizontaland vertical com- .ponents f lthe' appliedoscillographdeflection voltages originating {from the 'same signal"havev ,v a identical waveiformsni-I 'do n'otf detectiany avidio '1 Tfrequency modulation for-the operation 'of right and'left indicati0ns,but; as shall be' p "nt'ed out 1 Ehereinafter, subsequent detectiorioft' a'u'di frequency modulati'or'i" is feasible Without an of Figure 2bif the fixed antennareceiver is aural receptionreceiver is thereforeunnecess'ary which -is a decided advantage aircraft. 1 r :I shalltherefore :representthe voltage as am mliflcdbythe vertical antenna"axnplifier 20 and as applied to the vertical deflecting plates ,lfl'

mum .va1ue;.:. sumedby; the voltage evyand sin 21rft representsgtheSim-150idalv nature of the .1

s a if-carri r frequ n y, Limp essed pqg vertical antenna .II. The.signal-wicked up by the; loop antenna is amplified to a, voltage e1pplied to the orizontal deflecting plates l-iand N of theoscillographI9, where a is at v anetna' at; sinusoidal 'yoltage e1 assumes, and. Arepresents the electr-ital timephase difference between the similarvoltages grand e v applied :to thei plate s .of the cathode ray tube.This phase diiference A de- -pen ds on the degree-of mis'tuning of theloop. .It

well known in the artthat if two similar voltages are applied to the twopairs of plates ofa a straightlme if these voltages'are in phase or li80 'o ut ofzphase. If a phase displacement exists between. thesevoltages, the" image becomes an ellipse. It' is" preferable to have,anindication .Iwhich is astraight-lina, I therefore providea tuningvadjustment; to change therelative phase displacement ofthe loop Illvoltage as i applied to its amplifier 13 at. "input, {2, Thisituningyernier isa jvariable condenser I' l? connected acrossthe loop tuningcondenser. M as shownin Figure "l. The operatonmerely. adjusts. this vernier. I 4- to cau'sethe cathod'e ray image to become ,ast'raight line. Imay now represent e1 .3 E1sin21rft since thetime phase difi'erence A.the loop passes through the null or on -course position. Thus, if thedirection of the; signal is .as indicated by the bearing of the loop,the cathode-ray indication will he a yertical line 24. .When theapparent.directionisto the right, the

' imageis made to-deyiate towards the right or R, and similarly to L fora left indication, if the ,,,loop plane is maintained perpendicular tothe bearing. x r l t I Assuming that the pilot is flying radiallytowards a beacon station from which he is receiv- ,ing a signal, thenthe loop antenna, with its plane at right anglestothedirection of thesignal will I pick up no energy. On' the other hand thevertical antennavoltage 6v will Ice-impressed upon the cathode-ray tube l9 alone, andwill produce 'averticalline image on the screen as in Figure 2a.

"If now the pilot is thrown from his course, so

. .20 cathode-rayoscillograph, the resultantlmage is -th atlthetransmitting station is to the left of him,,then.theloopwill pickup'energy, the mag- .nitude of which is a function of the angle whichjtheloopmakes with the direction of the incoming signal. .The resultantbetween the magnitude of the vertical antenna lvoltage ev and the'magnitude of. the loop voltage 61 produces an image 26. as in Figure 3adeflected to the R quadflrant. The pilot then'knows that .heis flying on"abearing'itothe right of the beacon. If the pilot furtherdeflects fromhis. course, the magnitude of the signalpickedup by the loop willincrease, "horrespondmgly increasing the horizontal component voltage 21on the cathode ray tube l9 and thefirelsultant image deflection islthenmore to been adjusted to zero when the ima fi is 'a 7 straight line. aWhena signal is received b-y th is system,v the vertical antenna I I,being non-directionahcauses a vertical image as. 24 of Figure2a,.providing no resultantsignal is received by the loop antenna "theright. The pilot is thus apprised that he is moving further oifQcourseand towards the right of the, transmitting station. On theother hand,ifhe rotates his plane-so that it approaches the line of direction ofthe' receivedsignal, the signal I0. LWhenthe direction of thesignal;with.r'espect to} the angular position, of the loop antenna issuchwas, to cause .airesultant voltage' e across thehorizontaldeflectingplates l5 and 15,; the straight line image willassume .an angular positionfwithrespectto the vertical 'or normal posiefffFfigure 3a represents such a deflectionpf the imageifi to. theTrightof the .indicated normal osition cyan angleoa. This angle qais equal V ra ctan, e" arctan .is proportional to since these in-phase' deflectingcomponents. are F The quadrant of the deflection.

in,v quadrature. vinfltlxis-case towards R, is arbitrary and" is desi-gned to,,'correspond to a bearing to the' right of thejdesired coursewhenthe loop is maintained :in' the previous on-course position. Astraight line image "Will' be produced only when the volt- [ages-1e;andcv are in .phase'or 180 out of phase. However, when ,the apparatus isonce designed ,for'the image 26.;to deflect towards the R quad- ;rantwhen erand evare, forxexample, in-phase, thisjimage'will deflect towardstheleft orl quadimpressedupon theloop decreases in magnitude "and theresultant imag'eapproachesthe vertical. The pilotisthen apprised ofthefact that he is approaching the line of direction of thesignal .andis again onc ourse whenthe indication is a vertical, line,A-similar'consideration. is involved when he isflying oiT course towardsthe leftpf the transmittingstation, except that the loop receivesasignal 180 out of. phase with that corresponding to that received whenflying towardsthe right; and the image correspondingly deviates .towardsthe leftas line 21; Figure 3b, shows, We thus have normal or correctright and'left indications when navigating towards a and the resultant"magnitude of the deflection beacons Such an indicator is extremelyuseful "for f homingg i. e., flying to a destination trans mitter bykeeping the indicator image at zero or center. p i

In the case when the pilot is flying radially away from the transmittingstation-instead of rant. as. indicated. byfima e 217m Figure 3b havingthe corresponding, angle of inclination 0;, when the voltageslerand atbecome 18Of 01ltjof -phase. yJust such [a phase reversal occurs when.tieal image as 24 of. Figure. Zawill result.

approa'chingit, then the loop antennawith its plane ;at-:right angles tothe direction of the signal will again pick up no energy and a ver- 7 Ifnow :he is thrown to the right of the beacon, the loop antenna willpickup some energy, but since the orientation of the loopis reversed or fromthat condition hereinbefore described; the hori- 'zontal componentvoltage e1 will be 180 out or phase'withrespect to that "receivedhereinbefore whenthrown to the right and the image will have aninclination to the L instead of R quadrant. The pilot will thereforeassume that he is to the left of the incoming signal and therefore willturn his ship towards the right in order to turn tothegon-Coursedirection. He thussturns his ship further. .to the. right, increasingthe magnitude of the resultant signal'in; the loop and further;increasing the deflection inthe L quadrant. The pilot therefore willpromptly realize that he is swerving further frorn instead ofcloser tohis desired course, and is thus-lap prised of the fact that a reversedleft and rightindication is occurring, that he is flying on a;reciprocal or reversed bearing and that the .sig-, nal is coming fromthe rear rather than from: the

front of his ship.

' The phase angle A sume any value between 0:9Q, v seen by referring tothecurves in Radio -En-- gineeringj by Terman, page 49, Figure 2 3,-page 52, Figure 29 and page 54, Figure 30, ;and}.can

occur by merely mistuning the loop circuit;

However, it should be noted that a.l8 0 phase reversal by .mistuning isimpossible .because as;

seen from these curves the phase angle corresponding to A which isequalto ZorfL I can never even rcach 90. The snialhvernier' V tuningadjustment-1 1T in the loop circuit pro waste between ei andev This canhe;

' of the straight line image! 6 and-{therefore is dependent upon.thej-ratioj of given-"vertical componentev, increasing indicator videsmeans for properly phasing'theloop'volt-f age e1 with respect to theantenna'voltage, evgto,

the proper 0 or 180 phase relation; Since 7 mistuning cannot produce alflqf phase reversal;

the only possible conditionffor a straightline (when A equals 0) istobrinlg the "loop voltage phase to 0 or 180 to produce thieproper rightleft sense as designed for, and dependentgonlyi upon-the orientation ofthe loop in the fi'eld of the signal; Thus, when the cathode'ray screenpattern is a'straight'line, the phasing has bjeen properly adjustedirrespective? of any" previous c'onditions' of miStu'nin'gQ Thecomponentradio' frequency stages of the amplifiers l3 "andfZO produce a180; reversal in phaseof the voltage as the signallpasses througheachstageg 'l'hisj condition is taken care of by properly polarizing theloop antenna l-B with respectjto thehniplifier outputs to give normal or{correct right andleft so. designed will not change. 7 l a o i H Thepractical'functioning of my invention; is independent of any exact-'frequency'tuningf-of the amplifiers I 3 and 29' 'or' ofth'e loop antennaillby the comrnonltuning control-28. renipj ture variations ,ofth'eloop' antenna} mm; as; 2? F. per minute as may occur'in' an aircraftflight, will change the loop inductance and -cause mistuning of, theloops; However; any 'mist'uning';

hence mis'phas'ingof the component signal-Volt I ages 61 and 'evproducesanielliptic pattern on the screen 23 of the oscillograph fl instead 'of"a straight line i'mage'as is well know'n -in the art; The pilotlis thusimmediatelytapprised of-this mistuned condition, and adjusts'th'evernie'r c'on trol, Hi to make the image Onthe' screen 235a straightline. :-When.'the :pattern isa-straight positivei indication that. hisapparatus. is' functioning vproperly; because no defle'cted image is to,the directioniof :the :received signals'and'a a Yerticah liner;imageiis: accorclingly indicated? indications oh the oscillog-raph and-whenonce phase or 180 out ofg 'phase; Hen'cewhenaiver-f' tical straight lineindication appears uponsfthe screen 23, the indicated bearing isaccurate-and niediateiy. becomes aware o til x 11151 3 ve t al in i- 2d)occurs, irrespective ofjthe angu ar 'p 'o'si T vrectionalsensitivity-cit e ndica greate v when'the deviation romzvertieaa j Jziis' eat a givennumber.ofldegrees g offec urse. 5

{Theindicator angle-Qa'or (21 9f the-deviat on 1 equals tne amplified}loopi antennaflflisignal e amplified vertical antenna signal ev.-

deflections-ta orct zar obtained for correspond:-

ingly,increasingvalue-oi e15 For' increasd'ini dic'altor directionalsensitivity,"therforeythea tion is made {correspondingly greater.

' FOr'FgiVen' deflecting voltages ei and maximum defiectionalsensitivity of I the; lograph occurswhen: -='-the a'cceleratin'gfivoltalgce appliedsto the -"accelerating electrode is -a -m'ini mum:consistent with a reasonablepattern bril liancyi These considerationsare useful for-the optimum design of the apparatus; V t o The pilot willknow -when=his- $ourse is as indiL- v cated by the be'aringsq of theloop antenna in since; its plane is at, I that time perpendicularWhenheais directed towards? the right or left the signal T'SOllICE,:t-he7null reception point t the loopiisi'passed through and the signalvvh ch the loop; {receives causes 1 at corresponding right or leftdeviation of the indicatoneimage Ihe pilot then adjusts thelv'ernieri M:for a straight line image ,if mispha'sing is r; indicated; I-Ie haspossiplei without both a; vertical f and horizontal voltagecomponenteieandfema should the vertical antennaiil its '20-01[the-;verticai--defiectingwplates flianid 18 ome ere yel ade he.-opc'r tor im-i horizontal l the image (similar to 2 5 .of Figure 2is-.1ndicated of the positionlof'j the l o'o'p, Should the loo a of.theloop i 0:1 When no signal. is bein r,e-'

Ceivdior whenboth antenna systemsfhecome independentof anyvmistuning ormisphasingin' the apparatus. :Any variation ln'fflih overe-a-ll Jamplification of the signals d'ue :to jprfactical' Changes of supplyvoltage oroffothehelectfial parameters of. the apparatuswillmerelychange the height of the vertical line imagez tr (Figure 2a)for any-given inputs'ig'nal strengthl g; The-onbearing indication. ofthe v'erticalline im'age is always accurate as an indication,andritscame operativelyj defective; only arspot of light will .1 appearin the center'of the 'cathode rayi sc'ree'rf and: the j operatorwwouldnot then have T a; false I dication assom vnull f systemsiwould There lassociated wit the screen 23 a: scale 29 ha ing aIZeroEcenter"fand'tneietter R indi ,romheiera .aThe'rei is shown .in FigsJ 3a; 3b ain'd: l

30 another 7 scale 2,9 containing. zero: center; a

, forg v t Lvar'ying', length jde pendent uponj j tivelyidefec;

- Right? Left, anddivision markin'gsito con r spond to degrees 01f 'bow.l igure' iillus'tratesa 1 preferred arrangement to' facilitate readingof the indicator. Radiallin'es are printedor etched upon, the "glass"frontsurface 49of the cathode" A rectangularifo'rm is aflixe'd" raytube -2 31. V V vertically'and centrally over the zero or oncourse*line.It' contains a narrow; op'eningrto permit the operator to' concentrateupon a small central band of cathode ray'indicationsfthera through. Thiscentral porti'on is the nio st im -w' portant'band used by the pilot,and rapid observation of this region is-thus had. Pointers, 52 at thezero line are provided. The radial lines 56 may' be'numbered tocorrespond to degrees to R01" L off bow. A hole 5| in the centeris forobservation: of. the central spot.

The equipment may be calibrated 'to read actual degrees ofi bowasfollows: Automatic volume control, as is well known in the radio re--ceiver a i c ed zo m r th eamof both the loop amplifier and the-nomdirectional amplifier. This A. 'V. C. is'controlled by the'nondirectional receiver 'alone,\ ;.-and functions .to maintain a.predetermined ratio of Signals, A manual gain control is connected intotheyloop amplifier in any desired known .manner; Since the angle'ofdeflection of the image ,onthe screen depends on the ratio oftheamplification of the two amplifiers, as hereinbefore described, onemay proceed to calibrate thehdefiectionsito read actual degrees in the.following ,manner: .The

aircraft is directed .on course towards a chosen transmitting station asindicated. by the. apparatus. lBygmeans, of the ,usual navigational in-,

struments, such as a;,compass, the pilotgthen directs the aircraft awayfrom this direction'rbv adefinite amountgfor example, 15 degrees to theright; Adefiection to the rightwill be in dicated'on the cathode-raytubescreen; By op erating the manual gain control provided on -the loopamplifier =this deflection maysbe' changed untilit coincides with the15fdegree markin'gbn thescaleu The apparatus is thusicorrectly 'in-'dicating, and the, A. .VbCJwillHmaintain this 2,9 29, its;

y rigl'itand left indicating direction finder operates a'cathocle raytube ISas; anjindicator; This tube requires znegligible signal power forthe-operation of its'de'flecting plates. No energy its-thereforeabsorbed by'the indicator ill from the outputs'lza' and-22 of theamplifiers l3 and 20. "-I therefore connect audio unit 3!],which is adetector, andfif' desirable, may include an audio-amplifier across theoutput 22 offth fixed antenna l l amplifier 20. "Ihe-phone receivers3'lare'connected tothe output ofth audiorunit 30. A switch 39 serves toconnect the audio unit 30' to the apparatusshown in Figure 1;

.7 A modification of my invention makes use of superheterodyne-receptionand is illustrated in Figure 5. The balanced loop antenna Hl with itstuning condensers l4 and I4 are connected to the input 12%: the radiofrequency' amplifler l3'. The-output li is connected to the input 35 ofthe intermediate frequency amplifier 33 of the superheterodyne receiver.A signal from the beat frequency oscillator 32 is'introduced to l3,

' as indicated by the arrow 32 in Figure 5, The

output 33a is applied to the horizontal deflecting plates I5 and IE ofthe oscillograph I! as hereto- I fore, withthe voltage indicated-as e1.The fixed calibration under thes'e'op'erating conditions for a this andother. beacons. I There are. other visual .ind'ications' on the screenthat apprise the 'op'eratorwhen false hearing, indications are beingreceived, or ofwotl'ierv conditions of reception.- v

J If a difierent'sig'nalis received byifeaeh an- .tenna, the wave formoflth'evoltages eraiidiev applied. to the plates of theoscillograph'will also be difierent' a'nd. moving-or. complex geometricpatterns will iappeanon' the' screen when ofl'- course; The operatorthen "realizes that' th CUr-, responding on course hearing is false:Non-: periodic disturbance sf'such as heavy'static, will merely-appear'asfspots of lightt'of very short durationjaboutjthe screen are'a23 andWillTi'ri .0 wayinterreie withga bearing indicating line imagejgfIntermittent signals, fkeysignals, or.

afitenn'all is similarly connected to the input 2|. of the' rar'liofrequency amplifier which output 22? is connectedto the input 3'l oi theassociated intennediatejfrequency amplifier 34 of theisuperheterodyne.receiver forantenna H.

' The output'3 8 voltage ev'. is applied to the verticaldefiectingplates Ilfand I8 I of the oscillograph [SQ The commonbeat frequencyoscillator 32 is? coupled to both superheterodynereceivers in order toproduce intermediate frequency voltages e1! andfe f, of identicalfrequency. This is necessary in order toproduce a-fixed image upon thescreen ofth'e" cathoderay oscillograph, asis'well known in the 'art. Thetuning of the beat:frcquency oscillator 32 is controlled by the commontuning control 18 which tunes the radio frequency amplifier I 3 and 20and the loop tuning condenser 14. Thereception unit is shown connectedto the output of the fixed antenna intermediate frequency amplifier 34,through its switch 39; 1 l m V The' principle of;operation of thismodification is; similar to those discussed heretofor in connection withFigure '1. With'superheterodyne reception, however, morestable andgreater amplification. is practicable than with tuned radio frequencyreception. In this case; one frequency,

'thepi'ntermediate frequency, is. applied to the oscillograph I9imespective of the signal frequency andmay of the order of to severalhundred kilocycles; 'Inthe'. caseof Figure 1, the actual signal:frequencies are applied tooscillograph I 9,, range from 200m 1500kilncycles and higher. With the superheterodyne receivers, eacli radiofrequency and intermediateirequmcy stage successively reverses the:phase ofthe signal passing through it by 1-80,", For a givenarmamtusthat is designed for a 'pi-pper right andiett indicator sense, areversal in bearing of.18!) become apparent by atreversed iright'andleft indication. sense as :fherletofore described. The vernieriphasingcontrol 14 operates "as above, to

propefly='phase.the loop antennareceiued signal withirespect tothatreceived-by the fixed antenna. The phase displacement of the voltages c1and Ev are independent pf phase or the beat frequency. oscillatorvoltage, sincethis same voltage affects both amplifiers 33 andisimilarly and simultaneously. The phase displacement be+ responding toMl --'of tween er and evisthereforefmaintained"during themixing' step ofthe superheterodyne reception so that there is noinherentdiscrepancybetween this system and the tunedradio frequency sys-:: tem.

scribed my'jco-pending applicationise'rial No. 48,300, filed Novemberi5,1935, which matured: into Patent No.'2,062,129voniNovember 24; 1936;

In order, to reduce the acre-dynamic resistance of the loop, I employ astreamlined loop. as'd'e- Ni -1.1 of. the

' connected to the horizontal deflecting; platesfl'la.

.. put 980 -31 '2 of. the. non-directional antenna supere As thereexplained, in the majority of-cases tubu-i lar metallically shieldedloops have beenused; l

merely because they ofier: a.-convenient'jmethod of. mechanicalconstruction-.andsnot because'of anygreat advantagein shielding.Figurefishows. a loop wound with #33/38 Litz wire on asixinch diameterinsulated tubedl tand mountedwna rotatabl'e' base 42; within astreamlined housin 43.1 The loop drive shaft M is connected to the loopbase 42 at one end, and to the azimuth scale I and hand wheel, notshown,= at the':3oth er;-end.--

The end connections 45 andflfi toot-he loopcoilflii.

are brought through theloop'drive shaft 44, liv llq stream lined-housing43 is set upon the' ba se41.

which is connectedzby the mounting flange I18 to the body 49, of thevehiclepr aircraft upon which the apparatus is used. Housing 43 ispreferably of, insulating material. tion in distributed capacityand inradio fre; quency resistance of this loop antenna, using no metallicshield. Ihave foundits effectiveheight to be-fifty percent greaterthanan'eighteen inch shieldedrmetallic loop, and. its aero-dynamicresistance is /gs of such agloony Thehpusing 43 may be readily designedto withstand, eventhe rigors 'of a power dive by military aircraft. Thehousing 43 is rigidly mounted in position. K In antenna systems where;morethanjonef loop is mounted on an aircraft, this typ flof streamlinedhousing is 'particularlyiefie'ctive in minimizing? the tota'aero-dynamic resistance; particularly where theloopsareco-aiciah" Theis a 's eat ed e:

T Figure? showsa preferred diagrainniait al'ein-f bodiment of a completesystem designed'accord; ing to the'principles'of my inventiontf flh'eloop antenna 53, which may "ve'ry well' be the 'strearn lined loophereinheioredescribed, is" connected to the approach-'recedeswitch Mi"Y'Ifh center' tap 55 of the loop 53- isconnected-'to'groundrorsyrnmetrical electrical balancing- The terminals56' and El'areconnected tothe center posts of the double-poledouble-throw switch" 54. This switch heterodyneamplifier' is connected.toztheiverticat Q deflectingplates 82 andl83' ofithe tube 84r z signalfield strength of /2 microvolt perime may readily .be used to operatethis apparatuswith practical deflections. The electrodesiof thecathoderay tube 84' are connecte'd in a well-I known "manner. I operatethe superheterodyne receiverswithlan anode potential .of +2001V0lt5,

and the cathode ray tube with an anode potential" of +6001 volts... Thefocus control. 85 and m1 liancy control 66' are used 130- maintain'aaproper adjustment of the beam; Thexcircuits -of the superheterodynestages may be conventional [or connected in [any suitable well knownmanner; The switch 54' when connected tclthe .fapproach" side willcausezeroor on-course indications onl 1 the indicator when the aircraftapproachingior flyingtoward the radiobe'acon; With the switch connectedto the ,recede' position .such indica-:

flying from the beacons": Switch 54 is a reversing switchand is :usedto-r'evers'e theterminal con; nections of the loop toits amplifieit.-The 'pilot may thus atwill cause the equipment toindicate on-course'when either flyingj radially-towardsv or away'from"the beacon: The 'heatersare shown connected 'inpara'llel sets of' two heaters in series to"utilize the standardlZ-vdlt airplane supply with 6-Vo1t heater tubes;:An RIF. cathode-bias? gain of the loop indicator receiver. The operatormay thus control the "sensitivity of the angular deflections for a;particular' set of flying conditions: i A common automatic volumecontrol controlled by the non-directionalantenna amplifier may be. used-tomaintain a predetermined level of: amplificati'on in both amplifiersby circuit arrange-.

ments-well-kno'wn in the radio receiver 'art and therefore-,not'shown inFigure? to avoid complication; -Thisautomatic volume control would vmaintain a calibrated deflectional. sensitivity f the-indicatorafter thedirectional sensitivity control 81 is-adjusted in conjunction withaknown I flying deviation, as 'hereinbefore set forth;

54 serves to reverse'the "eonnections'of -this loop v as connected"across the loop' tuning-condense'r 53.

Condenser 58' isthe Vernier phasing control core loop Signal isintroduced to the firstiRz; Epentode amplification stagefifl; A second-R; F. pentode stage 50 is cascadediwith stage .5,9;and its coutputisintroduced to the first detector. stage Bl.; jIfhe,

non-directional antenna 62 is tuned .to the signal connected, to theinpu Of; t e. B'samp ification stage 63. Aloeat frequency oscilla or thecommon oscillator for both amplifier trains.

the i er v are eas b t? "R i .i,n 9il? to m m z mQ P1ig-: s irl ng n eer 5 9 1 54 as 599%? h t d to t e rrfi per iu P i r e fir or stages 6!endfii meueesarel intermediate frequencies whichKare passed thr gh there nQnsi s-tuee than has J and TN o the r s ectiv h ghin inte atefrequency stages U Figuresland The input is ue at" lla 'nigt s d weVarious methods for; coupling this lo'sillatorlto (i5v'udio-receivercorrespondin to' 30 of Figures' '1 and 5'-isf shown in apreferredv form I Figure 'Z as followsz A-small coil 88 loosely .coupledto theoutput' I. F. transformer 15 ofthe non-directional amplifier.Since" intermediate frequency signals of thelorder of l50-vclts areintroduced'at t-he output points andi8 I to the cathode rayo'scillograph'fl l, it is essential that i g H precautions-must be takento avoid feedback and other intercoupling troubles I, when using suhselquent audio-detection and" amplification. The-- signal pickedup-by-con88 is introducedltof theaudioe or second detectorstage 89where' it idemo'dulated and I. Fiamplifier andserves as an 15F; trap to eifectivelyby-pass any I. F. components that have reached that point to avoidspurious effects.

* when audio-reception isj not esired' loop superheterodyne amplifieris;

mg" control 8'l'is' employedasshown to vary'ythe; r

f urtherfcoupled to the audioamplifier stage 90s I have provided aninductance fll with a capacitance 82 connected in series I 'WitHitacross' the output of the seconddetector stage 89. "jThisseriesecircuit -iit and SZ ispre; V tuned-to theintermediate frequencyused inthe g e, 1 output ofcthe audio-amplifier "is connected in nyl.suitable manner to telephone jacks foraudio- 1 reception. i'Ifheswitchss'isuseam interrupt the y heater yo-ltage, supply to the audio-stages39 and It is Althoughfin illustrating this principle, I have realizedthat since a 'small. percentage of the available'I. F. signal energy isnecessary tOOPBI'e; ate thi audio-receiver section, thecconn'ection'ofrtion of any received signal, without in any waytheheaters or thissection by means-of switchc'93; will permitithe operator toli'sten'totheniodulaa affecting the. right and left indications" ofv the c cathoderay tube. Design; .precautions'iz-must' be takentol avoid feedback andintercouplingibe-r tween the .two amplifiers. Suchprecautiohsare wellknown tortheart; and are necessary where two; such high gain unitsare soclosely inter- --lFigure 8 shows a circuit connecting the cathode raytube; 84 in another preferredmanner, sozthat the high-potentialelectrodes and the correspond. ing deflecting plates are connected toground. and thecathode isconnected to .600 voltau". I

To decrease the capacity coupling between the horizontal and verticaldeflectinggplates of the. cathode ray tube I provide screens 94 insertedbetween them as illustrated in .Fig. These screens mayhave a. lattice01'. grid structure, and

are :circuitally connected in amanner similarqto the ordinary screengridof atetrode orpentodel employed aioop and vertical antenna; two ampliflers, a cathode ray tube; and particular circuit connections; itwillbeunderstood thatI am not to be limited by these examples, but only as setforth-in theappended claims.

1. In. a directional system; a loopantenna for receiving signalswvaryingin magnitude in ac-- cordance with theirelation of the plane of the loopto thedirection to the transmitting station: anon-directional antennaforfreceiving signals from the same station; an amplifier connected tosaid loopantenna; 'anramplifier connected. to said non-directionalantennaf a cathoderay tuberhaving a flrstj and second pair or deflectorplates; circuit-connections from "the output said loop antenna amplifierto one set of said deflector electrodes of said cathode ray tube;circuit connections from the output of said nondirectiona1 antennaamplifie r't'o the other set of said deflector eieotrodesof said cathoderaytube for produc The D. .C. electrostatiopotential of these screens941wi1l correspondto that of the'defiecting plates but will still be atground A. Capotential. HFor airplane dashboard use, the regular. co1nstruction of a cathode ray tubeis inco-nveniently A long. Figureillustrates sucha tube 8 4. bent over on itself to'reduce. its; over-alllength by half;

The; elements are correspondingly numbered ga inFigure 8. Severaldeflecting plates 95 are con nected to the high-potential sourceoithetube. These plates 95, at the same "potential as -;the acceleratinganode, will deflect the electron. beam 96 m the mannerillustrated,around the-bent portion 91 of tube 841 The deflecting plates [8; 19, 82and '83 are ,placedbeyondthe last defleeting plate 95 in the finalcoursehof the beam 96 before it hits the screen. g 1 u From the above itwill now be clear that; I have discovered a right and left indicatingdirection finder which isdcpendent for its directional acouracy onlyupon {the angular position of a single loopiantenna withrespect to thesignal source ing directional indications corresponding to the directionto the transmitting station and means for bringing the ignals receivedin the radiation field through said loop and through saidnondirection'alantenna into phase with each other at' aid deflectingplates of said cathode ray 2. In a directional system; a loop antennamounted on a moving vehicle and rotatable with respect to thedirectionto the transmitter staand is completely independent of anyaccidental variation in conditions or adjustments of; the 'circuit. "Allprevious right and left indicating di rection finders have depended uponthe compari:

son of the relative pick-up. or two antennae whereas myright and leftindicatingsystem dcpends I for its directional indications only upon theabsolute pick-upof a single loop antenna and utilizes thecharige-over ornull reception characteristic of the loop for its indications; Iprovidefor-"independent amplification of the loop and non-directional antennaesignals, and introduce the'ioutputs of the respective amplifiers, at the1 original or av'reduced. frequency, to two' 'corne spending setsqofdeflecting plates" of a cathode raytube.v 'It' will be seen that thevertioal vand.

loop antennae signals. are in no Way intercom:

nected 'or intercoup'led except at the cathode ray tube. I thus avoidall the'difiiculties of this: Phasin and other unbalancing possiblewithprevious systems where the loop and erticalantennae signals-'rnust'becombined in a particular manner. c. g., to pr oduce a'cardioid receptionpatg term-before introduction} to the amplifier. ,I'lfur thermore have 6con tant independent visualv "in dic'a tions oi the condition and"relative combination of the received signals as the direction oftravel'ofthe vehicle changes with respect to the direction to thetransmitting tation of the received signal for receiving signalsintheradiation fieldvarying in magnitude inaccordance with the relation of-the plane of the loop to the direction to the transmitting station; anon-directional antenna forreceivingsignais from the same station; an;amplifier connected to said loop antenna; an amplifier connected to saidnon-directional antenna; a common' controi for said amplifiers; acathode ray tube having a first and second pair of 'defiectingplat'es';circuit connections from the output of said loop antenna amplifier toone pair or said deflecting'plates circuit connections from the outputof saidnon-di rectional antenna amplifier to the other pair ofdeflecting plates for producing directional indications corresponding tothe direction'to the transmitting stationwith respect 'to' the plane ofthe loop. a p 3.",In (a directional system; a loop antenna mounted on amoving vehicle and rota-tablewith respectto the direction to thetransmitter station I relation f the-plane of the Ioop'to the directionhonor the two antennae and amplifier-compo in previous systems theielS,no

way of'reali'zingsuch factors. 1

of the received signals. as the direction of travel of the vehiclechanges withtrespect :to the direction to. :the transmitting station ofthe received signalfor receiving signals inthe radiation .neld varyingin 'magnitude in, accordance withine to {the transmitting station a nondirectional n n airor'recnv ng signals ircm the same-std tion; onamplifier connected to said loop antenna anamplifier connected to; saidnonnirecti on'a-l antjeinna; afcathoderay tube havi'hga first and secondpailof deflecting plates; circuit connections'fron the output of'saidloop plates; circuit connection's from the output of saidnonadirectional antenna amplifierte the othe fpair of saiddefiectingplates; meansfor translatingthe variationsin amplitude ofthe re? delvedsignals intodire'ctional indications on-said tube of the direction tothe transmitting statiorr Withiespectto the plane ofthe 'loop ire o t na5am g i P1 14km a -directi 'nalsystem tionof the receivedsignals as thedirection of travel of the Vehicle changes with respect to'the directionto the transmitting station of the received signal for receiving signalsvarying in magnitude in accordance with the relation of the plane of theloop to the directionlto the transmitting station; a non-directionalantenna for receiving signals from the same station; an amplifierconnected to said loop antenna; an amplifier connected to saidnon-directional antenna; a commoncontrol for said amplifiers; a cathoderay tube having a first and second pair of defleeting plates; circuitconnections from the output of said loop antenna amplifier to one pairof said deflecting plates; "circuit. connections a. e, v, X .lq emounted on a moving vehicle-and "rotatable'jwith respect to ,thedirection to thetransmittersta ofai predete rminedr intensity andcorresponding to the radio-signals upon said first set'of deflectin'gZplates-iorproducing a -null reference line indication comprisinganon-directional antenna; a first amplifierpandcircuitwconnections'irom'said first amplifier to said first set of deflecting plates; adirectional antenna for receiving-said radio signals with an intensityvarying in accordance with the angular position of said directionalantenna with respect to the direction of said transmitter; means forimpressing the directional signals upon said second set of deflectingfrom the output of said non-directional antenna I amplifier to the otherpair of said deflecting plates; means for translating. the variations inamplitude of the received signals into directional indications on saidtube of the direction to the transmitting station with respect to theplane of the loop free of directional ambiguities.

5. In a directional system; a loop antenna mounted on a moving vehicleand rotatable with respect to the direction to the transmitter stationof the received signals as the direction of travel of the vehiclechanges with respect to the direction to the transmitting station of thereceived signal for receiving signals varying in magnitude in accordancewith the relation of the plane of the loop to the direction to thetransmit ting station; a non-directional antenna for receiving signalsfrom the samestation; a superheterodyne amplifier for each antenna; acathode ray tube having a first and second pair of deflecting plates;circuit connections from the output of said loop antenna amplifier toone pair of said deflecting plates; circuit connections from the outputof said non-directional antenna amplifier to the other pair of saiddeflecting plates for producing directional indications corresponding tothe direction to the transmitting station with respect to the plane ofthe loop.

6. In a directional system; aloop antenna plates for controlling theangular. deflection of V 7 said indication from said reference inaccordance s with the angular'deviation of said directional antenna"with respect to said transmitter comprising asecond amplifier, circuit"connections from said second amplifier to said second set of deflectingplates, and means for varying the de flectional sensitivity of saidindication; and a common tuning controlfor said amplifiers.

8. In a system for indicating the direction of a transmitter of radiosignals, an'indicatorfcom-* prising a cathode ray tube having afirst'and second set of deflecting plates disposed in an an gularrelation; a fluorescent *screen', and .means .i a for generating anelectron beam; means for 1m:

pressing signals of a-predetermined intensity and corresponding to the;radio' signals upon said j U first set of deflecting plates forprcducing'a null reference line indication on said screen comp'risj inganon-directional antenna, a firstamplifier, and circuit connectionsfromsaid first amplifier to said first set of deflecting plates; adirectional antenna for receiving said'radio signals with'an intensityvarying in accordance-with the angular position of said directionalantennawith respectto the direction of said transmitter; means forimpressing the directional signals upon said second set of deflectingplates for controllingthe angular-deflection oi saidindication from saidreference in accordance with the angular deviation of said directionalantenna with, respect to said transmitter comprising a second amplifier,

mounted on a moving vehicle and rotatable'with respect to the directionto the transmitter station of the received signals as thedirection oftravel of the vehicle changes with respect to the direction to thetransmitting station of the received signal for receiving signalsvarying in magnitude in accordance with the relation of the 7 plane ofthe loop to the direction to the transmitting station; a non-directionalantenna for receiving signals from the same station; a superheterodyneamplifier' for each antenna; a common control for each amplifier; acathode ray tube having a first and second pair of deflecting plates;circuit connections from the output of said loop antenna amplifier toone pair of said deflecting plates; circuit connections from the outputof said non-directional antenna amplifier I to the other pair of saiddeflecting plates for producing directional indications corresponding tothe direction to the transmitting station with respect to the plane ofthe loop.

7. In a system for indicating the direction of a transmitter of radiosignals, an indicator comprising a cathode ray tube having a first andcircuit connections from said second amplifier to said second set ofdeflecting plates, andv means for varying the deflectional sensitivityof said indication; and means for controlling the time phase relationbetween said signals to bring them I into substantial time phaserelation to produce a substantially straight line indication on saidscreen comprisinga variablelcondenser.

9. In a'system for indicatifg the angular relation, a fluorescentscreen, and mean for generating'an electron beam; means for impressingsignals of a predetermined intensity and corresponding to the radiosignals upon said first set of deflecting plates'for producing a nullrefer I ence line indication on said screen comprising a non-directionalantenna, a first amplifier, and

circuit connections from said first amplifier to said first set ofdeflecting plates; ardirectional antenna for receiving said radiosignals with aniintensity varying in accordance with the angularposition of said directional antenna with 'redirection of saidtransmitter; means signals upon said 1 second set of deflecting platesfor controlling the angular deflection of said indication from saidspect to the for impressing the directional second 'set' of deflectingplates disposed in an: angular *relationymeans for impressing' signalsdirectionof a transmitter of radio signals, an indicator com- 1 prisinga cathode ray tube having a first and"; second set of deflecting platesdisposed in an referenee infac'cordance with the angular devia tion ofsaid::directiona1 antenna; with respect to;

said transmitter comprising a second amplifier; a variablecondenser fortuning said directional antenna, circuit connections from :said secondiamplifier to said second set of' deflecting plates, and meansfor Varyingthe defiectional sensitivity variable oondenser.

'of said} indication; means for; controlling the time phase relationbetween said signals to produoe-a.

substantially straight line in diea tionyon said screencomprising; a.manually operable ernier condenser \ioonneote d in parallel across vsaidED AR J.

